Orient the ItsyBitsy PCB so the microUSB connector is facing the small opening on the side of the 3D printed case. Place the board over the case and press it down into it into the case. Three walls should clip onto the edges of the PCB. Depending on how tight the tolerances are, you may need to firmly press down on the PCB.
The push button can be fitted into the square post with the leads on the sides. It should have a snug fit and hold in place. Orient the wires so they're routed along the outside of the post. Be careful not to bend the leads.
You'll want to position the wiring along the inside of the case so they're neatly routed. The Perma-Proto PCB should have enough room to fit in between the ItsyBitsy board and side walls of the case. The two JST plugs and vibration sensor wiring should be fitted over the opening.
Place the 3D printed button actuator over the rubber piece of the switch. Orient the cover so the button cutout is lined up with button. Then, bring the two parts together and firmly press them together to snap it shut. You should get a nice click. If you can't get the cover to fully close, you may need to adjust the PCB or wiring.
Test NeoPixel Strips
Now we can test out the NeoPixel strips. You'll want to double check the wires are soldered to the right connections before powering on the circuit. Pin #10 ought to be wired to the DATA INPUT, not the output, as indicated on the strip itself with a little arrow icon pointing away from the pads. If everything checks out, plug in a USB battery to the ItsyBitsy board. You can shake the vibration sensor to trigger the NeoPixel animations. Use the button to cycle between 3 different modes.